|Title:||Characterisation of experimentally induced and spontaneously occurring disease within captive bred dasyurids|
|Authors:||Lindsay, Scott Andrew|
|Publisher:||University of Sydney.|
Faculty of Veterinary Science.
|Abstract:||Neosporosis is a disease of worldwide distribution resulting from infection by the obligate intracellular apicomplexan protozoan parasite Neospora caninum, which is a major cause of infectious bovine abortion and a significant economic burden to the cattle industry. Definitive hosts are canid and an extensive range of identified susceptible intermediate hosts now includes native Australian species. Pilot experiments demonstrated the high disease susceptibility and the unexpected observation of rapid and prolific cyst formation in the fat-tailed dunnart (Sminthopsis crassicaudata) following inoculation with N. caninum. These findings contrast those in the immunocompetent rodent models and have enormous implications for the role of the dunnart as an animal model to study the molecular host-parasite interactions contributing to cyst formation. An immunohistochemical investigation of the dunnart host cellular response to inoculation with N. caninum was undertaken to determine if a detectable alteration contributes to cyst formation, compared with the eutherian models. Selective cell labelling was observed using novel antibodies developed against Tasmanian devil proteins (CD4, CD8, IgG and IgM) as well as appropriate labelling with additional antibodies targeting T cells (CD3), B cells (CD79b, PAX5), granulocytes, and the monocyte-macrophage family (MAC387). Toluidine blue labelling of mast cells complemented results. Effective labelling was not obtained with CD79a, interleukin-4, interferon-γ, or MHCII antibodies. Descriptions of pathology such as the site and extent of tissue necrosis in S. crassicaudata resemble those reported in immunocompromised rodent models. The exception is the lack of major involvement of the brain and associated neurological signs. Immunohistopathologic findings suggest the dunnart host cell response resembles that described in eutherians – strongly neutrophilic with fewer macrophages focused on sites of tissue necrosis, with a predominantly T cell nature to any lymphoid response inclusive of CD4 positive T helper cells. Intracellular parasite replication is frequently observed in the absence of a detectable host cellular response. More sensitive alternative techniques such as real time polymerase chain reaction using effective cytokine labelling is recommended to further define the host response to neosporosis. Active surveillance of disease to further define the animal model involved collecting cadavers over 28 months from the dunnart colony maintained at the University of Sydney. An additional 66 S. crassicaudata and S. macroura animals were examined. Of the 28.3% of animals diagnosed with a disorder of growth (n=15), 80.0% were diagnosed with a malignancy (n=12), and the most frequently diagnosed neoplasm was squamous cell carcinoma. Lesions were seen on the rostral mandible (2), pouch (2), distal limb (1), and tail (1) and five of six of these tumours were diagnosed in S. macroura. The single squamous cell carcinoma diagnosed in the pouch of an S. crassicaudata showed a distinctive verrucous growth pattern, prompting consideration of a viral causation. Immunohistochemical investigation of carcinomatous proliferations using multiple bovine papillomavirus markers and an antibody targeting the p16 cell protein found no supportive evidence for a viral association. Additional colony pathology included single or multicentric nodular pyogranulomatous or suppurative disease (botryomycosis) – sometimes a comorbidity of carcinoma. In S. crassicaudata eight cases of gastric dilatation were also identified – with and without trichobezoar formation. Collection and examination of specimens from the colony is ongoing.|
|Type of Work:||Masters Thesis|
|Type of Publication:||Masters of Veterinary Science (M.V. Sc.)|
|Appears in Collections:||Sydney Digital Theses (Open Access)|
|lindsay_s_thesis.pdf||6.07 MB||Adobe PDF|
Items in Sydney eScholarship Repository are protected by copyright, with all rights reserved, unless otherwise indicated.